What is the difference between a class 3 and a class 4 toilet?I am considering the Toto one piece with the 3" pipe. It will go in a cabin where I drain the water when we aren't here, including emptying the tank and adding RV anti-freeze to tank and bowl. Is there any reason I could not use the Toto in this situation? (my early Universal-Rundle has been fine with the antifreeze, but doesn't flush well, thus I will replace it.)Your web site is superb. Thanks